New Podspec Help file

I've included it as a gist so you can see it in it's entirety https://gist.github.com/orta/6070878

I've taken the old help file and grouped a lot of the spec attributes together to make the whole thing a bit easier to read. I've given all the copy a look-over to see if it can be terser and more direct. I think I've got most of the core bits down but I'm a native english speaker and you guys aren't so it'd be useful to know if I've removed something that was useful.